Handrails for escalators, moving walkways and other transportation apparatus are usually produced in indefinite lengths. A conventional handrail has three main components, namely the main body of the handrail, which is commonly formed from a rubber or other thermoset material; a plurality of steel, reinforcing cables, which act as a stretch inhibitor to define a neutral axis and to give the handrail a desired stiffness in a longitudinal direction, while enabling it to flex in a vertical direction, so as to be capable of travelling around pulley wheels, drive mechanisms etc; and a slider fabric that is commonly bonded to the handrail within a T-shaped channel on the bottom of the handrail, the function of the slider being to provide a low coefficient of friction between the handrail and a supporting and correspondingly shaped guide. Conventional handrails also commonly included various layers of fabric reinforcement.
Conventionally, handrails have been produced in a piece wise fashion. As the main material of the handrail body is a thermoset material, this has caused little difficulty. After production of each section within a mold, the handrail is moved forward, and the next section formed after it.
For a particular application, to form a splice at an installation site, a so-called "field splice", an appropriate length of handrail is selected, and the ends prepared for splicing together. Commonly, this involves cutting the ply containing the steel cables and interlacing them. The slider fabric is cut appropriately. The ends are then assembled in a mold, the mold is filled with fresh material, and the mold is then heated, to cause the material to set.
In production of the handrail, if the length required is known, then in the factory a "factory splice" can be made. A length of handrail is produced with the ends left uncured, so that an invisible, smooth splice can be made using a production mold.
Proposals have been made for forming handrails for escalators and the like from a thermoplastic polymeric material, such as polyurethane, and one example is shown in U.S. Pat. No. 4,618,387 (Fisher et al.) assigned to Westinghouse Electric Corp. It is first noted that the practical utility of this method is questioned, since the patent only shows and describes a C-shaped section for a handrail having the main body formed from the elastomeric material and a plurality of steel cables or other inextensible members. No mention is made of the fabric slider that, as a practical matter, is required for any conventional handrail. It is not seen how even a test loop of handrail could have been made and tested, if the slider was not present. To applicant's knowledge, there is no practical way of bonding this slider to the handrail after formation of a complete handrail loop, nor indeed after the forming of any length of handrail. It has, to applicant's knowledge, to be formed with the handrail at the time that the other elements of the handrail are assembled.
In any event, the main proposal in this U.S. Pat. No. 4,618,387 is to cut the two ends of the handrail square, and then heat fuse them together. It is not clear how this is intended to be effective, but it is suggested that as the interfaces are short, only a small amount of elastomeric material will extrude from the periphery of the joint and require removal.
This method by itself is believed to be almost certainly inadequate, and indeed, a test sample prepared by the present inventors showed that a distinct plastic hinge developed at the break in the steel cables. A large part of the strength of a handrail is derived from the steel reinforcing cables. A simple, square butt joint would require the elastomeric material to provide the strength across the joint, and this would be unacceptable. To allow for this, the disclosed method also provides for cutting a number of longitudinally extending, parallel grooves between the existing cables. Short lengths of the cables are then placed in the grooves and a thin sheet of material is disposed over the grooves. Heat is then applied to the sheet on the joint area to cause the sheet to melt and flow into the grooves to surround them. Again, it is not entirely clear how it is intended for this to be achieved, nor how the correct profile would be maintained. Such a technique is clearly impossible when the slider is present and if the slider is to be continuous, and it is clear that this method can only readily be practised on a handrail assembly without the slider fabric.
A further disadvantage to this technique is that, in the area of the joint, there will be, approximately, twice the density of reinforcing cables as in the rest of the handrail, giving the joint area a stiffness and flexing characteristic quite different from the rest of the handrail, which it is believed would result in unusual and undesirable wear characteristics. It is suggested this can be alleviated by feathering the joint, but this would simply relieve the abrupt change in stiffness, rather than eliminating it.
The problem of splicing together the ends of a selected length of an endless member is known in many other fields of technology. In particular, there are many proposals in the conveyor belt field for splicing belts together. U.S. Pat. No. 3,481,807 is one example, which shows various interlacing techniques. It shows cutting of reinforcing cables so that the junctions in individual cable runs are staggered along the length of the belt. It also shows this characteristic for outer cables, combined with overlapping or interlacing of ends of inner cables. This method is intended to be applied to a rubber belt, with a covering material that can be replaced and vulcanized. It does not address the problem of applying this technique to a belt formed from a thermoplastic material, particularly the problem that the whole body of a thermoplastic belt could melt and run away if it is heated without being contained.